1-aminopyridinium dyes as sensitizers in electrophotographic layers

ABSTRACT

1-Aminopyridinium dyes are useful for sensitizing photoconductive compositions used in electrophotographic layers. The dyes are heat and light bleachable so that undesirable color imparted to background areas of the image bearing element by the dyes is easily removable. Such bleaching increases the visual contrast of the reproduction.

United States Patent Contois 51 Apr. 25, 1972 [54] l-AMINOPYRIDINIUMDYES AS SENSITIZERS IN ELECTROPHOTOGRAPHIC LAYERS [72] Inventor:Lawrence Edward Contois, Webster, N.Y.

[73] Assignee: Eastman Kodak Company, Rochester,

[22] Filed: Oct. 3, 1969 211 Appl. No.: 870,485

[52] US. Cl ..96/l.6, 96/1 .7, 260/240.4 [51] Int. Cl ..G03g 5/06, 603g5/08 [58] Field of Search ..96/1 .6, 1.7, 102,140;

[56] References Cited UNITED STATES PATENTS 2,839,403 6/1958 Knott..260/240.4X

Primary Examiner-Charles E. Van Horn Attorney-William H. J. Kline, JamesR. Frederick and Fred L. Denson [5 7] ABSTRACT l-Aminopyridinium dyesare useful for sensitizing photoconductive compositions used inelectrophotographic layers. The dyes are heat and light bleachable sothat undesirable color imparted to background areas of the image bearingelement by the dyes is easily removable. Such bleaching increases thevisual contrast of the reproduction.

10 Claims, No Drawings l-AMINOPYRIDINIUM DYES AS SENSITIZERS INELECTROPHOTOGRAPHIC LAYERS This invention relates to electrophotography,and in particular to novel sensitized photoconductive compositions andelements having coated thereon such compositions.

The process of xerography, as disclosed by Carlson in U.S. Pat. No.2,297,691, employs an electrophotographic element comprising a supportmaterial bearing a coating of a normally insulating material whoseelectrical resistance varies with the amount of incident actinicradiation it receives duringv an imagewise exposure. The element,commonly termed a photoconductive element, is first given a uniformsurface charge, generally in the dark after a suitable period of darkadaptation. It is then exposed to a pattern of actinic radiation whichhas the effect of differentially reducing the potentialof the surfacecharge in accordance with the relative energy contained in various partsof the radiation pattern. The differential surface charge orelectrostatic charge image remaining on the electrophotographic elementis then made visibleby contacting the surface with a suitableelectroscopic markingmaterial. Such marking material or toner, whethercontained in an insulating liquid or on a dry carrier, can be depositedon the exposed surface in accordance with either the charge pattern orthe absence of charge pattern as desired. The deposited marking materialmay then be either permanently fixed to the surface of the sensitiveelement by known means such as heat, pressure, solvent vapor, or thelike, or transferred to a second element'to which it may similarly befixed. Likewise, the electrostatic charge image can be transferred to asecond element and developed there.

Various photoconductive insulating materials have been employed in themanufacture of electrophotographic elements. For example, vapors ofselenium and vapors of selenium alloys deposited on a suitable supportand particles of photoconductive zinc oxide held in a resinous,film-forming binder have found wide application in present-day documentcopying applications.

Since the introduction of electrophotography, a great many organiccompounds have also been. screened for their photoconductive properties.As a result, a verylarge-number of organic compounds are known topossess some degreev of photoconductivity. Many organic compoundshaverevealed a useful level of photoconduction and have beenincorporated into photoconductive compositions. Optically clear organicphotoconductor-containing elements having desirable electrophotographicproperties can be especially useful in electrophotography. Suchelectrophotographic elements maybe exposed through a transparent base ifdesired, therebyproviding unusual flexibility in equipment design. Suchcompositions, when coated as a film or layer on a suitable support alsoyield an element which is reusable; that is, it can be used to formsubsequent images after residual toner from prior images has beenremoved by transfer and/or cleaning.

Although some of the organic photoconductors comprising the materialsdescribed are inherently light sensitive, ,their. degree of sensitivityis usually low and in the short wave-length portion of the spectrum sothat it is common practicezto add materials to increase the. speed andto shift the sensitivity toward the longer wave-length portion of thevisible spectrum. Increasing the spee systems into the visible region ofthe spectrum has severaladvantages: it makes available inexpensive andconvenientlight sources such as incandescent lamps; it reduces exposuretime;

it makes possible the recording of a wide range of colors-in propertonal relationship, and allows projection printing through variousoptical systems. By increasing the speed through the use of sensitizers,photoconductors which would,

otherwise have been unsatisfactory are useful in processes where highspeeds are required such as document copying.

A primary disadvantage associated with the. use of sensitizers is that,because they are usually highly colored,- they may impart undesirablediscoloration to the entire photoconductive element. As a result, animage developed directly on and shifting the sensitivity of such a thesurface of the element can be viewed only with great difficulty becauseof the low visual contrast between toned and untoned areas. Furthermore,such an element bearing a developed image is generally unsuitable foruse as a master for the making of further reproductions.

It is therefore an object of this invention to provide novel sensitizedphotoconductive elements.

It is another object of this invention to provide novel sensitizedphotoconductive compositions.

it is a further object of this invention to provide a process forbleaching the novel sensitized photoconductive elements.

These and other objects are accomplished with photoconductivecompositions containing a photoconductor and a laminopyridinium dye as asensitizer for the photoconductive composition. According to thisinvention, it has been found that when l-aminopyridinium dyes are usedin photoconductive compositions, an enhanced sensitization effect isrealized. Photoconductive compositions which do not contain thesensitizers of this invention frequently do not produce good qualityimages when used in element form in an electrophotographic process.

An advantage resulting from the employment of the laminopyridiniumsensitizers herein in photoconductive compositions is that good qualityimages are obtainable when the compositions are coated on supports andused in electrophotographic processes. Another advantage is that theintensity of the color imparted to the coated compositions by thesensitizers can be substantially reduced i.e., bleached, by

subjecting the elements to actinic radiation, e.g., a light exposure ofat least 6 X 10 foot-candle-seconds. Also, elements containingthesensitizers of this invention can be bleached by heating to atemperature of at least about C. for at least about 15 seconds.Generally, there is no practical advantage in using exposures of greaterthan l0 foot-candle-seconds or heating to temperatures in excess of 250C. for more than 1 hour. Bleaching can be accelerated by combining heatwith light exposure. The most rapid bleaching is obtained by using theabove heating conditions while simultaneously exposing the element tolight giving an illuminance of at least 4,000 foot-candles. Sourcescombining ultraviolet with visible light are particularly effective,e.g. tungsten-halogen lamps.

The fact that the sensitizers used in the element can be bleached issignificant from thestandpoint of being able to view an image which isdeveloped directly on the surface of the.electrophotographic element andalso being able to use the visible-image-bearing element as a masterfrom which further prints can be made on a wide variety of :materials.Bleaching causes substantial reduction of the optical opacity in thebackground areas, thus permitting the uses described above. In order toobtain these advantages using many other known sensitizers which arehighly colored, the electrostatic charge imagemust be transferred to areceivingelement and developed there or, if developed on the surface ofthe electrophotographic element, the visible image must be transferredto a receiving sheet before it can be viewed.

The preferred l-aminopyridinium sensitizing dyes of this invention havethe following formula:

l l :L-L: C=O R7 m wherein R, and R, when taken separately can be a.analkyl group preferably having one toeight carbon atoms such as methyl,ethyl, propyl, butyl, etc. including a substituted alkyl radical such asaralkyl, e.g., benzyl; hydroxyalkyl such as hydroxypropyl,hydroxyethyl,etc.;

b. an acyl group; e. g.,

2( lH)-pyridylidene)ethy1idene]-2l-1-pyrrido[ 1,2-a]pyrimidine-2,4(3H)-dione XI 3-[( l-acetanilido-4-p-tolyl-2( ll-l)-pyridylidene )ethylidene] 2H-pyrrido[ 1,2-a]pyrimidine-2,4(3H)- dioneX11 3-[( l-pyridyl-4-p-tolyl-2( lH)-Pyridy1idene)ethy-1idene]21-1'pyrido[ l,2-a]pyrimidine-2,4(3H)-dione Electrophotographicelements of the invention can be prepared with any photoconductivecompound and the sensitizers of this invention in the usual manner,i.e., by blending a dispersion or solution of the photoconductivecompound together with a binder, when necessary or desirable, andcoating or forming a self-supporting layer with the photoconductivecomposition. Generally, a suitable amount of the sensitizing compound ismixed with the photoconductive coating composition so that, afterthorough mixing, the sensitizing compound is uniformly distributedthroughout the desired layer of the coated element. The amount ofsensitizer that can be added to a photoconductor-incorporating layer togive effective increases in speed can vary widely. The optimumconcentration in any given case will vary with the specificphotoconductor and sensitizing compound used. In general, substantialspeed gains can be obtained where an appropriate sensitizer is added ina concentration range from about 0.0001 to about 30 percent by weight ofthe film-forming coating composition. Normally, a sensitizer is added tothe coating composition in an amount from about 0.005 to about 5.0percent by weight of the total coating composition.

The sensitizers of this invention improve the electrical speeds ofcompositions containing a wide variety of photoconductors includinginorganic photoconductors such as zinc oxide, titanium'dioxide, cadmiumsulfide and the like, organic photoconductors including organometallicphotoconductors and mixtures thereof.

Typical additional photoconductors useful with the binders ofthisinvention are described below.

A. Arylamine photoconductors including substituted and unsubstitutedarylamines, diarylamines, nonpolymeric triarylamines and polymerictriarylamines such as those described in U.S. Pat. Nos. 3,240,597 and3,180,730.

B. Photoconductors represented by the formula wherein 2 represents amononuclear or polynuclear divalent aromatic radical, either fused orlinear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or asubstituted divalent aromatic radical of these types wherein saidsubstituent can comprise a member such as an acyl group having from oneto about six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), analkyl group having from one to about six carbon atoms (e.g., methyl,ethyl, propyl, butyl, etc.), an alkoxy group having from one to aboutsix carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or anitro group; Z represents a mononuclear or polynuclear monovalent orpolynuclear monovalent aromatic radical, either fused or linear (e.g.,phenyl, naphthyl, biphenyl, etc.); or a substituted monovalent aromaticradical wherein said substituent can comprise a member, such as an acylgroup having from one to about six carbon atoms (e.g., acetyl,propionyl, butyryl, etc.), an alkyl group having from one to about sixcarbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy grouphaving from one to about six carbon atoms (e.g., methoxy, propoxy,pentoxy, etc.), or a nitro group; O can represent a hydrogen atom or anaromatic amino group, such as ZNl-1; b represents an integer from 1 toabout 12, and L represents a hydrogen atom, a mononuclear or polynucleararomatic radical, either fused or linear (e.g., phenyl, naphthyl,biphenyl, etc.), a substituted aromatic radical wherein said substituentcomprises an alkyl group, an alkoxy group, an acyl group, or a nitrogroup, or a poly(4-vinylpheny1) group which is bonded to the nitrogenatom by a carbon atom of the phenyl group, these materials being morefully described in U.S. Pat. No. 3,265,496.

C. Polyarylalkane photoconductors including leuco bases of diaryl ortriarylmethane dye salts, 1,1,1-triarylalkanes wherein the alkane moietyhas at least two carbon atoms and tetraaryl' methanes having an aminogroup substituted in at least one of the aryl nuclei attached to thealkane and methane moieties of the latter two classes of photoconductorswhich are non-leuco base materials; and also other polyarylalkanesincluded by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, analkyl group, or an aryl group, at least one of D, E and G containing anamino substituent, the aryl groups attached to the central carbon atombeing preferably phenyl groups, although naphthyl groups can also beused including substituted aryl groups containing substituents such asalkyl and alkoxy typically having one to eight carbon atoms, hydroxy,halogen, etc., in the ortho, meta or para positions, ortho-substitutedphenyl being preferred; the aryl groups can also be joined together orcyclized to form a fluorene moiety, for example; the amino substituentcan be represented by the formula wherein each R can be an alkyl grouptypically having one to eight carbon atoms, a hydrogen atom, an arylgroup, or together the necessary atoms to form a heterocyclic aminogroup typically having five to six atoms in the ring such as morpholino,pyridyl, pyrryl, etc.; at least one of D, E and G preferably being ap-dialkylaminophenyl group, when .1 is an alkyl group, such an alkylgroup more generally has one to seven carbon atoms, these materialsbeing more fully described in U.S. Pat. No. 3,274,000, French Pat. No.1,383,461 and in U.S. Ser. No. 627,857 filed Apr. 3, 1967 by Seus andGoldman.

D. Photoconductors comprising 4-diarylamino substituted chalcones havingthe formula:

wherein R 1 and R are each phenyl radicals including substituted phenylradicals, R preferably having the formula:

wherein R and R, are each aryl radicals, aliphatic residues of one to 12carbon atoms such as alkyl radicals preferably having one to four carbonatoms, or hydrogen; particularly advantageous results being obtainedwhen R is a phenyl radical including a substituted phenyl radical andwhere R is diphenylaminophenyl, dimethylaminophenyl or phenyl, thesematerials being more fully described in Fox application U.S. Ser. No.613,846,filed Feb. 3, 1967, now U.S. Pat. No. 3,526,501.

E. Non-ionic cycloheptenyl compounds which may be substituted withsubstituents such as:

i. an aryl radical including substituted as well as unsubstituted arylradicals,

2. a hydroxy radical,

3. an azido radical,

4. a heterocyclic radical having five to six atoms in the heterocyclicnucleus and at least one hetero nitrogen atom, and including substitutedand unsubstituted heterocyclic radicals, and

5. an oxygen linked cycloheptenyl moiety.

The substitution on the cycloheptenyl nucleus occurs at an unsaturatedcarbon atom when the cycloheptenyl moiety is a conjugated triene with noaromatic structure fused thereto. However, if there is at least onearomatic structure fused to the cycloheptenyl moiety, then thesubstituents are attached to a saturated carbon atom. Additionalphotoconductors within this class are included in one of the followingformulae:

where E and G can be either:

I. a phenyl radical,

2. a naphthyl radical,

3. a heterocyclic radical having five to six atoms in the heterocyclicnucleus and at least one hetero nitrogen atom,

4. a hydroxyl radical, or

5. an oxygen containing radical having a structure such that theresultant cycloheptenyl compound is a symmetrical ether;

0, can be any of the substituents defined for E and G above and isattached to a carbon atom in the cycloheptenyl nucleus having a doublebond; (R and R,,,), (R,, and R (R, and R and (R and R,,) are togetherthe necessary atoms to complete a benzene ring fused to thecycloheptenyl nucleus; these compounds being more fully described inU.S. Ser. No. 654,091 filed July 18, 1967, now U.S. Pat. No. 3,533,786.

F. Compounds containing an nucleus including:

1. unsubstituted and substituted N, N-bicarbazyls containingsubstituents in either or both carbazolyl nuclei such a. an alkylradical including a substituted alkyl radical such as a haloalkyl or analkoxyalkyl radical,

b. a phenyl radical including a substituted phenyl radical such as anaphthyl, an aminophenyl or a hydroxyphenyl radical,

c. a halogen atom,

d. an amino radical including substituted as well as unsubstituted aminoradicals such as an alkylamino or a phenylalkylamino radical,

e. an alkoxy radical,

f. a hydroxyl radical,

g. a cyano radical,

h. a heterocyclic radical such as a pyrazolyl, carbazolyl or a pyridylradical; or

tetra-substituted hydrazines containing substituents which aresubstituted or unsubstituted phenyl radicals, or heterocyclic radicalshaving five to six atoms in the hetero nucleus, suitable results beingobtained when all four substituents are not unsubstituted phenylradicals, i.e., if at least one substituent is a substituted phenylradical or a heterocyclic radical having five to six atoms in the heteronucleus. Other tetra-substituted hydrazines include those having thefollowing formula:

nun

5 wherein both D, and G, are either substituted phenyl radicals orheterocyclic radicals. These compounds are more fully described in U.S.Ser. No. 673,962 filed Oct. 9, 1967.

G. Organic compounds having a 3,3-bis-aryL-2-pyrazoline nucleus which issubstituted in either five-member ring with the same or differentsubstituents. The l and 5 positions on both pyrazoline rings can besubstituted by an aryl moiety including unsubstituted as well assubstituted aryl substituents such as alkoxyaryl, alkaryl, alkaminoaryl,carboxyaryl, hydroxyaryl and haloaryl. The 4 position can containhydrogen or unsubstituted as well as substituted alkyl and aryl radicalssuch as alkoxyaryl, alkaryl, alkaminoaryl, haloaryl, hydroxyaryl,alkoxyalkyl, aminoalkyl, carboxyaryl, hydroxyalkyl and haloalkyl. Otherphotoconductors in this class are represented by the followingstructure:

wherein:

D D,', J, and J can be either a phenyl radical including a substitutedphenyl radical such as a tolyl radical or a naphthyl radical including asubstituted naphthyl radical,

E E G G,,, L and L, can be any of the substituents set forth above andin addition can be either a hydrogen atom or an alkyl radical containingone to eight carbon atoms. These organic photoconductors are more fullydescribed in U.S. Ser. No. 664,642 filed Aug. 31, I967, now U.S. Pat.No. 3,527,602.

H. Triarylamines in which at least one of the aryl radicals issubstituted by either a vinyl radical or a vinylene radical having atleast one active hydrogen-containing group. The phrase vinylene radical"includes substituted as well as unsubstituted vinylene radicals and alsoincludes those radicals having at least one and as many as threerepeating units of vinylene groups such as wherein n is an integer offrom 1 to 3. Groups which contain active hydrogen are well known in theart, the definition of this term being set forth in several textbookssuch as Advanced Organic Chemistry, R. C. Fuson, pp. l54-l57, John Wiley& Sons, 1950. The term active hydrogen-containing group" as used hereinincludes those compounds encompassed by the discussion in the textbookcited above and in addition includes those compounds which containgroups which are hydrolyzable to active hydrogen-containing groups.Typical active hydrogen-containing groups substituted on the vinyleneradical of the triarylamine include:

1. carboxy radicals,

2. hydroxy radicals,

3. ethynyl radicals,

4. ester radicals (e.g.,

lawn-1 ntwherein R is alkyl or aryl) including cyclic ester radicalswherein R is a cyclic alkylene radical connected to a vinylenecombination such as is found in coumarin derivatives),

. carboxylic acid anhydride radicals,

. semicarbazono radicals,

. cyano radicals,

.acryl halide radicals (e.g.,

c1 etc), and

9. amido radicals (e. g.,

wherein R is a hydrogen atom, an alkyl group or an aryl group).

Other active hydrogen-containing groups include substituted andunsubstituted alkylidyne oximido radicals. Photoconductors included inthis class can be represented by the following structure:

R10 B17 in wherein:

l. Ar and Ar are each a phenyl radical including a substituted phenylradical such as a halophenyl radical, an alkyl phenyl radical or anaminophenyl radical,

2. Ar, is an arylene radical including a substituted arylene radicalsuch as a phenylene radical or a naphthylene radical,

3. R and R are each hydrogen, a phenyl radical including a substitutedphenyl radical or a lower alkyl radical preferably having one to eightcarbon atoms,

4. X is either:

a. an active hydrogen-containing group such as a carboxy radical, anacyl halide radical, an amido radical, a carboxylic acid anhydrideradical, an ester radical, a cyano radical, a hydroxy radical, asemicarbazono-radical, an ethynyl radical, or a methylidyne oximidoradical or b. hydrogen provided that when X is hydrogen "R and R arealso hydrogen, and

5. n is an integer of l to 3.

The arylene nucleus can be substitutedin any position:by the vinyl orvinylene moiety. However, when Ar isphenylene, particularly good resultsare obtained if the substitution occurs in the para position. Thesematerials are more fully described in U.S. Ser. No. 706,800 filed Feb.20, 1968,.now U.S. Pat. 3,567,450.

I. Triarylamines in which at least one of thearyl radicals issubstituted by an active hydrogen-containing, group. The term activehydrogen-containing group" has-the same meaning as set forth above andagain includes those compounds encompassed by-the discussion in thetextbook and additionallyincludes those compounds which contain groupswhich are hydrolyzable to active hydrogen-containinggroups. Typicalactive hydrogen-containing groups which are substituted on an arylradical of the triarylamine include:

1. carboxy radicals,

2. hydroxy radicals,

3. ethynyl radicals,

4. ester radicals (e.g.,

Are

wherein R is an alkyl or an aryl group),

5. lower alkylene hydroxy radicals (e.g., having one to eight carbonatoms,

6. carboxylic acid anhydride radicals,

7. lower alkylene carboxy radicals (e.g., having two to eight carbonatoms),

8. cyano radicals,

9. acryl halide radicals (e.g.,

l -d-o1 etc.),

10. amido radicals (e.g.,

II C-N wherein R is a hydrogen atom, an alkyl group or an y g p),

11. lower alkylidyne oximido radicals having one to eight carbon atomsincluding substituted alkylidyne oximido radicals (e.g.,

wherein R is hydrogen or a lower alkyl radical),

12. semicarbazono radicals, and

13. arylene carboxy radicals including substituted arylene carboxyradicals (e. g.,

wherein D and E are phenyl or lower alkyl radicals. Photoconductorsincluded in this class can be represented by the following structure:

wherein:

a. Ar and Ar are each a phenyl radical including a substituted phenylradical such as a halophenyl radical, an alkyl phenyl radical or anamino phenyl radical,

b. Ar is an arylene radical including a substituted arylene radical suchas a phenylene radical or a naphthylene radical, and

c. X is an active hydrogen-containing group such as a car- 'boxyradical, an acyl halide radical, an amido radical, a carboxylic acidanhydride radical, an ester radical, a cyano radical, a semicarbazonoradical, a hydroxy radical, an ethynyl radical, a methylidyne oximidoradical or a phenylene carboxy radical.

These materials are more fully described in U.S. Ser. No.

706,780 filedFeb. 20, 1968, now U.S. Pat. No. 3,567,450.

.1. Organo-metallic compounds having at least one aminoaryl substituentattached to a Group IVa or Group Va metal atom. The metallicsubstituents of this class of organic hotoconductors are Group IV orGroup Va metals in accordance with the Periodic Table ofthe Elements(Handbook of Chemistry and Physics, 38th edition, pp. 394-) and includesilicon, germanium, tin and lead from GrouplVa and phosphorus, arsenic,antimony andbismuth from Group Va. These materials can be substituted inthe metallo nucleus with a wide variety of substituents but at least oneof the substituents must be an amino-aryl radical. The amino radical canbe positioned anywhere on the aromatic nucleus, but best results areobtained if the aryl moiety is a phenyl radical havingthe amino group inthe 4 or para position. Typical substituents attached to the metalnucleus include the following:

where E, 0,, L and Q can be:

a. a hydrogen atom,

b. an aryl radical including unsubstituted as well as substituted arylradicals such as a phenyl radical, a naphthyl radical, adialkylaminophenyl radical, or a diarylaminophenyl radical,

c. an alkyl radical having one to eight carbon atoms,

d. an alkoxy radical having one to eight carbon atoms,

e. an aryloxy radical such as a phenoxy radical,

f. an amino radical having the formula wherein R and R can be hydrogenatoms or alkyl radicals having one to eight carbon atoms, or g. aheterocyclic radical having five to six atoms in the hetero nucleusincluding at least one nitrogen atoms such as a triazolyl, a pyridylradical, etc.,

T is an amino radical such as an alkylamino radical having one to eightcarbon atoms or an arylamino radical such as a phenylamino radical;

Ar is an aromatic radical such as phenyl or naphthyl;

M", nd M g are the same or different Group [Va metals;

M, is a Group Va metal;

D, can be any of the substituents set forth above for E G L and Q and inaddition can be a Group IVa organometallic radical or, when taken withE, an oxygen atom or a sulfur atom;

J 5 can be any of the substituents set forth above for E 0,, L and Q andin addition can be when taken with E, an oxygen atom or a sulfur atom.These materials are described in US. Ser. No. 650,664 filed July 3,1967.

K. Any other organic compound which exhibits photoconductive propertiessuch as those set forth in Australian Pat. No. 248,402.

Representative organic photoconductors useful in this in- 5 ventioninclude the compounds listed below:

TABLE I diphenylamine dinaphthylamine N,N-diphenylbenzidine N-phenyll-naphthylamine N-phenyl-Z-naphthylamine N,N'-diphenyl-p-phenylenediamine 2-carboxy-5-chloro-4-methoxydiphenylaminep-anilinophenol N ,N -di-2-naphthyl-p-phenylenediamine 4,4'-benzylidene-bis-( N ,N-dimethyl-m-toluidine) triphenylamine N,N ,N ,N-tetraphenyl-m-phenylenediamine 4-acetyltriphenylamine4-hexanoyltriphenylamine 4-lauroyltriphenylamine 4-hexyltriphenylamine4-dodecyltriphenylamine 4,4 -bis( diphenylamino )benzil 4,4 -bis(diphenylamino)benzophenone polyadipyltriphenylaminepolysebacyltriphenylamine polydecamethylenetriphenylamine poly-N-(4-vinylphenyl )diphenylamine poly-N-( vinylphenyl )-a,a-dinaphthylamine4,4-benxylidene-bis( N,N-diethyl-m-toluidine) 4 ,4'-diamino-4-dimethylamino-Z ,2 '-dimethyltriphenylmethane 4 ,4 '-bis(diethylamino )-2,6'dichloro-2 ,2 '-dimethyltriphenylmethane 4 ,4 -bis(diethylamino )-2 2 dimethyldiphenylnaphthylmethane 2 ,2 '-dimethyl-4,4,4 -tris(dimethylamino )triphenylme tha 4' ,4 '-bis(diethylamino)-4-dimethylamino-2 ,2 -dimeth yl' triphenylmethane 4 ,4-bis( diethylamino )-2-chloro-2 ,2 -dimethyl-4-dimethylaminotriphenylmethane 4 ,4 '-bis( diethylamino)-4-dimethylamino-2 ,2 ',2

trimethyltriphenylmethane 4 ,4 -bis( dimethylamino )-2-chloro-2 ',2'-dimethyltriphenylmethane 4 ,4 -bis( dimethylamino )-2 ,2'-dimethyl-4-methoxytriphenylmethane bis(4-diethylamino)- l l l-triphenylethane bis( 4-diethylamino )tetraphenylmethane 4 ',4 -bis(benzylethylamino )-2 ,2 -demethyltriphenylmethane 4 ,4 '-bis(diethylamino )-2 ,2 '-diethoxytriphenylmethane 4,4-bis( dimethylamino)-ll 1 -triphenylethane 1-(4-N,N-dimethylaminophenyl)- l l -diphenylethane4-dimethylaminotetraphenylmethane 4-diethylaminoetraphenylmethane 4,4'-bis( diphenylamino)chalcone 4-diphenylamino-4 -dimethylaminochalcone4-dimethylamino-4 '-diphenylaminochalcone 4,4 -bis( dimethylamino)chalcone 4,4'-bis( diethylamino)chalcone 4-diethylamino-4-diphenylaminochalcone 4-diphenylaminochalcone 4-dimethylaminochalcone 4-diphenylaminochalcone 4 '-dimethylaminochalcone bis-[ 5-( 5 H-dibenzo[a,d cycloheptenyl) ether 5-hydroxy-5H-dibenzo[a,d]cycloheptene l- {5-(5H-dibenzo[a,d]cycloheptenyl)} -4,5-dicarbomethoxyl ,2 ,3triazolepoly(vinyl butyral); polyacrylic and methacrylic esters, such aspoly(methy methacrylate), poly(n-butyl methacrylate), poly(isobutylmethacrylate), etc.; polystyrene; nitrated polystyrene;polymethylstyrene; isobutylene polymers; polyesters, such ascopoly[ethylene-co-alkylenebis(alkyleneoxyaryl)phenylenedicarboxylate];phenolformaldehyde resins; ketone resins; polyamides; polycarbonates;polythiocarbonates; poly[ethylene-co-isopropylidene-2,2-bis(ethyleneoxyphenylene)terephthalate]; copolymers of vinylhaloarylates and vinyl acetate such as poly(vinyl mbromobenzoate-covinyl acetate); etc. Methods of making resins of this type have beendescribed in the prior art, for example, styrene'alkyd resins can beprepared according to the method described in U.S. Pat. Nos. 2,361,019and 2,258,423. Suitable resins of the type contemplated for use in thephotoconductive layers of the invention are sold under such trade-namesas Vitel PE-lOl, Cymac, Piccopale 100, Saran F220, Lexan 105 and Lexan145. Other types of binders which can be used in the photoconductivelayers of the invention include such materials as paraffin, mineralwaxes, etc. Mixtures of these binders may also be employed.

Solvents useful for preparing coating compositions with thephotoconductors of the present invention can include a wide variety oforganic solvents for the components of the coating composition. Forexample, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbonssuch as methylene chloride; ethylene chloride; and the like; others,such as tetrahydrofuran and the like, or mixtures of such solvents canadvantageously be employed in the practice of this invention.

In preparing the coating compositions useful results are obtained wherethe photoconductor substance is present in an amount equal to at leastabout 1 weight percent of the coating composition. The upper limit inthe amount of photoconductor substance present can be widely varied inaccordance with usual practice. In those cases where a binder isemployed, it is normally required that the photoconductor substance beresent in an amount from about 1 weight percent of the coatingcomposition to about 99 weight percent of the coating composition. Apreferred weight range for the photoconductor substance in the coatingcomposition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support canvary widely. Normally, a coating in the range of about 0.001 inch toabout 0.01 inch before drying is useful for the practice of thisinvention. The preferred range of coating thickness was found to be inthe range from about 0.002 inch to about 0.006 inch before dryingalthough useful results can be obtained outside ofthis range.

Suitable supporting materials for the photoconductive layers of thepresent invention can include any of a wide variety of electricallyconducting supports, for example, various-conducting papers; aluminumpaper laminates; metal foils such as aluminum foil, zinc foil, etc.;metal plates, such as aluminum, copper, zinc, brass, and galvanizedplates; vapor deposited metal layers such as silver, nickel or aluminumon conventional film supports such as cellulose acetate, poly(ethyleneterephthalate), polystyrene and the like conducting supports. Anespecially useful conducting support can be prepared by coating asupport material such as poly(ethylene terephthalate) with a layercontaining a semiconductor dispersed in a resin. Such conducting layersboth with and without insulating barrier layers are described in U.S.Pat. No. 3,245,833. Likewise, a suitable conducting coating can beprepared from the sodium salt of a carboxyester lactone of a maleicanhydride-vinyl acetate copolymer. Such kinds of conducting layers andmethods for their optimum preparation and use are disclosed in U.S. Pat,Nos. 3,007,901, 3,245,833 and 3,267,807.

The elements of the present invention can be employed in any of thewell-known electrophotographic processes which require photoconductivelayers. One such process is the aforementioned xerographic process. Asexplained previously, in a process of this type the electrophotographicelement is given a blanket electrostatic charge by placing the sameunder a corona discharge which serves to give a uniform charge to thesurface of the photoconductive layer. This charge is retained by thelayer owing to the substantial insulating property of the layer, i.e.,the conductivity of the layer in the dark. The electrostatic chargeformed on the surface of the photoconducting layer is then selectivelydissipated from the surface of the layer by exposure to light through animage-bearing transparency by a conventional exposure operation such as,for example, by contact-printing technique, or by lens projection of animage, etc., to form a charge image in the photoconducting layer. Byexposure of the surface in this manner, a charge pattern is created byvirtue of the fact that light causes the charge to be conducted away inproportion to the intensity of the illumination in a particular area.The charge pattern remaining after exposure is then developed, i.e.,rendered visible, by treatment with a medium comprisingelectrostatically attractable particles having optical density. Thedeveloping electrostatically attractable particles can be in the form ofa dust, e.g., powder, a pigment in a resinous carrier, i.e., toner, or aliquid developer may be used in which the developing particles arecarried in an electrically insulating liquid carrier. Methods ofdevelopment of this type are widely known and have been described in thepatent literature in such patents, for example, as U.S. Pat. No.2,297,691, and in Australian Pat. No. 212,315. In processes ofelectrophotographic reproduction such as in xerography, by selecting adeveloping particle which has as one of its components, a low-meltingresin, it is possible to treat the developed photoconductive materialwith heat and cause the powder to adhere permanently to the surface ofthe photoconductive layer.

The present invention is not limited to any particular mode of use ofthe new electrophotographic materials, and the exposure technique, thecharging method, the transfer (if any), the developing method, and thefixing method as well as the material used in these methods can beselected and adapted to the requirements of any particular technique.

EXAMPLE 1 A composition in the form of a dope consisting of thefollowing materials is coated at a wet thickness of 0.004 inch on apoly(ethylene terephthalate) film support having a conducting layer ofthe sodium salt of butyl ester lactone made from vinyl acetate maleicanhydride copolymer as in Example 1 of U.S. Pat. No. 3,260,706:

Photoconductor. 3-(4-diphenylaminophenyl) propionic acid 0.5 g. Binder.poly(4,4'-isopropylidenebisphenyleneoxyethylene-co-ethyleneisophthalate) l.5 g. Sensitizerl 0.0l g. Dichloromethane 9.60 g.

in a darkened room the surface of the photoconductive layer so preparedis charged to a potential of about +600 volts under a corona charger.The layer is then covered with a transparent sheet bearing a pattern ofopaque and light-transmitting areas and exposed to the radiation from anincandescent lamp with an illumination intensity of about 75metercandles for 12 seconds. The resulting electrostatic charge image isdeveloped by cascading over the surface of the layer negatively chargedblack thermoplastic toner particles on glass bead carriers. Thebackground area of the reproduction is a deep red, causing the developedimage to have very poor visual contrast. The developed image-bearingelement is then exposed to the radiation from a 500 watt G.E. lamp (No.PH/RFLZ) at a distance of 5 inches for 25 seconds. The deep red colorbleached to a pale yellow and the developed image has a substantiallyimproved visual contrast.

EXAMPLE 2 Example 1 is repeated except bleaching is accomplished byheating the developed image-bearing element at 140 C. for 60 seconds;The bleached element has an improved visual contrast compared to theunbleached element.

EXAMPLE 3 Examples 1 and 2 are repeated, simultaneously heating to 125C. and exposing the developed image bearing element to the 500 wattsource to cause bleaching. Substantial bleaching to a pale yellow iscaused within 15 seconds. The developed image is easily viewable.

EXAMPLE 4 Example 1 is repeated using the following photoconductingcompounds in place of 3-(4-diphenylaminophenyl) propionic acid:

a. 4-carboxytriphenylamine,

b. 3-(4-diphenylamino)phenyl methyl propionate and c.bis-4-diethylaminotetraphenylmethane.

The binder is replaced with poly(vinyl-m-bromobenzoate-covinyl acetate).After bleaching each of the elements in the described manner, goodquality images having good. visual contrast are obtained in eachinstance.

EXAMPLE 5 Example 1 is repeated except the sensitizer is omitted. Nodevelopable electrostatic charge image is obtained.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

lclaim:

1. A photoconductive composition comprising a photoconductor and al-aminopyridinium dye sensitizer for said composition, said sensitizerhaving the formula:

wherein:

Q- represents the non-metallic atoms necessary to complete a five to sixmembered heterocyclic nucleus; R and R when taken separately are eachselected fromthe group consisting of a. an alkyl group, b. an acylgroup,

. hydrogen, an aryl group, a heterocyclic nucleus containing five to sixmembers in the hetero nucleus, and f. when taken together represent theatoms necessary to complete a five to six membered heterocyclicnucleus;R; and R are each selected from the group consisting of a. a hydrogenatom, b. an alkyl group, and c. an aryl group; m is a positive integerfrom 1 to 2; and L is a methine linkage. 2. The composition of claim 1whereinthe photoconductor is an organic compound.

3. The composition of claim 1 further comprising a polymericfilm-forming binder.

wherein:

Q represents the non-metallic atoms necessary to complete a five to sixmembered heterocyclic nucleus;

R and R when taken separately are each selected from the groupconsisting of a. an alkyl group,

b. an acyl group,

c. hydrogen,

d. an aryl group,

e. a heterocyclic nucleus containing five to six members in the heteronucleus, and

f. when taken together represent the atoms necessary to complete a fiveto six membered heterocyclic nucleus;

R and R are each selected from the group consisting of a. a hydrogenatom, b. an alkyl group,and c. an aryl group;

m is a positive integer from 1 to 2; and

L is a methine linkage.

5. The element of claim 4 wherein the photoconductive compositioncontains a polymeric film-forming binder.

6. An electrophotographic element comprising a support having coatedthereon a layer of a photoconductive composition comprising:

a. about 10 percent to about 60 percent by weight based on saidphotoconductive composition of an organic photoconductor,

b. a film-forming polymeric binder for said photoconduc tor and c. 0.005percent to about 5 percent by weight based on said photoconductivecomposition of a sensitizer comprising 3-[( l{N-methylanilino}-4,6-di-p-tolyl-2( lH)-PYridylidene]ethylidene)-2H-pyrido[ 1 ,2-a]pyrimidine-2,4-

( 3H)-dione.

7. The element of claim 6 wherein said organic photoconductor is3-(4-diphenylaminophenyl)propionic acid.

8. A process for bleaching an image-bearing electrophotographic elementhaving a layer of a photoconductive composition containing al-aminopyridinium dye sensitizer comprising the step of heating theelement to a temperature of at least about C. for at least about 15seconds, said sensitizer having the formula:

wherein:

Q represents the non-metallic atoms necessary to complete a five to sixmembered heterocyclic nucleus;

R and R when taken separately are each selected from the groupconsisting of a. an alkyl group, b. an acyl group, c. hydrogen, (1. anaryl group, e. a heterocyclic nucleus containing five to six members inthe hetero nucleus, and

f. when taken together represent the atoms necessary to wherein:

complete a five to six membered heterocyclic nucleus;

R; and R are each selected from the group consisting of a. a hydrogenatom, b. an alkyl group, and c. an aryl group;

in is a positive integer from 1 to 2; and

L is a methine linkage.

9. The process of claim 8 further comprising simultaneously exposing theelement to an illuminance of at least 4,000 footcandles during theheating step.

10. A process for bleaching an image-bearing electrophotographic elementhaving a layer of a photoconductive composition containing al-aminopyridinium dye sensitizer, comprising the step of subjecting theelement to actinic radiation of at least about 6 X 10foot-candles-seconds and to which the element is sensitive, saidsensitizer having the formula:

Q represents the non-metallic atoms necessary to complete a five to sixmembered heterocyclic nucleus; R and R when taken separately are eachselected from the group consisting of a. an alkyl group, b. an acylgroup, c. hydrogen, 10 d. an aryl group,

e. a heterocyclic nucleus containing five to six members in the heteronucleus, and f. when taken together represent the atoms necessary tocomplete a five to six membered heterocyclic nucleus; R and R are eachselected from the group consisting of a. a hydrogen atom, b. an alkylgroup, and c. an aryl group; Re In is a positive integer from 1 to 2;and l L is a methine linkage.

2. The composition of claim 1 wherein the photoconductor is an organiccompound.
 3. The composition of claim 1 further comprising a polymericfilm-forming binder.
 4. An electrophotographic element comprising asupport having coated thereon a photoconductive composition comprisingan organic photoconductor and a sensitizer for said photoconductivecomposition having the formula:
 5. The element of claim 4 wherein thephotoconductive composition contains a polymeric film-forming binder. 6.An electrophotographic element comprising a support having coatedthereon a layer of a photoconductive composition comprising: a. about 10percent to about 60 percent by weight based on said photoconductivecomposition of an organic photoconductor, b. a film-forming polymericbinder for said photoconductor and c. 0.005 percent to about 5 percentby weight based on said photoconductive composition of a sensitizercomprising3-((1-(N-methylanilino)-4,6-di-p-tolyl-2(1H)-pyridylidene)ethylidene)-2H-pyrido(1,2-a)pyrimidine-2,4-(3H)-dione.
 7. The element of claim 6wherein said organic photoconductor is3-(4-diphenylaminophenyl)propionic acid.
 8. A process for bleaching animage-bearing electrophotographic element having a layer of aphotoconductive composition containing a 1-aminopyridinium dyesensitizer comprising the step of heating the element to a temperatureof at least about 140* C. for at least about 15 seconds, said sensitizerhaving the formula:
 9. The process of claim 8 further comprisingsimultaneously exposing the element to an illuminance of at least 4,000foot-candles during the heating step.
 10. A process for bleaching animage-bearing electrophotographic element having a layer of aphotoconductive composition containing a 1-aminopyridinium dyesensitizer, comprising the step of subjecting the element to actinicradiation of at least about 6 X 104 foot-candles-seconds and to whichthe element is sensitive, said sensitizer having the formula: